Lighttpd Multiple Instances on same machine

I want to setup 2 instances of Lighttpd: test and production instances (i.e. on different ports). Do I need to install a whole new instance or just reconfigure the existing one? For the two instances I'd need different document roots. I tried the method given in Lighttpd book by Andre Bogus but it didn't work out for me. The machine is Ubuntu 9.10. Please let me know how to proceed.